The purpose of this project is two-fold: (1) to create a realistic model system for exocytosis, with particular emphasis on its relevance to transmitter release at synapse; (2) to reconstitute, in lipid bilayer membranes, ion permeability systems existing in biological membranes. The system to be investigated is the interaction of phospholipid vesicles with lipid bilayer membranes. The basic questions are: will such vesicles fuse with the bilayer from one side and release their contents on the other side, and at what rate does this occur? What is the effect of lipid composition (both of the vesicles and the membrane) on the rate of this process? How is this rate controlled both by the surface charge of the vesicles and the membrane, and by the concentration of divalent cations (such as Mg ions and Ca ions) in the medium? The answers to these questions will directly bear on the mechanism by which Ca ion stimulates transmitter release at presynaptic terminals (e.g., the neuromuscular junction) and stimulates exocytosis from such cells as the chromaffin cells of the adrenal medulla and the islet cells of the pancreas. In addition, by first incorporating into the vesicles naturally occurring ion-conducting channels (e.g., the acetylcholine receptor from electroplax), one can then, via the fusion process, incorporate these channels into the bilayer membrane. Having done so, one can then examine their properties by classical electrophysiological techniques in a particularly simple system. Furthermore, this system offers a unique and sensitive assay for these channels during and after isolation and purification procedures.